Severus Snape - Wikipedia

In an interview,[1] Rowling described Snape's character as an "antihero". She has said that she drew inspiration for Snape's character from a disliked teacher from her own childhood,[2] and described Snape as a horrible teacher,[3] saying the "worst, shabbiest thing you can do" as a teacher is to bully students.[4] However, she does suggest in the books that he is generally an effective teacher.[5] Although Rowling has said that Gilderoy Lockhart is her only character that she "deliberately based on a real person",[6] Snape was reportedly based, at least in part, on John Nettleship, who taught Rowling chemistry and employed her mother as an assistant at Wyedean School near Chepstow.[7][8][9] Rowling based Snape's given name on "Severus Road" in Clapham,[10] and his surname is borrowed from the name of a village in England.[11][12] In a 1999 interview[13] and again in 2004,[6] Rowling singled out Snape as one of her favourite characters to write.

Rowling was less forthcoming about Snape than she was for other characters, because his true loyalties and motivations were not revealed until the final book.[14] However, she hinted numerous times at Snape's important role, suggesting that people should "keep their eye on Snape".[2][15] In 1999, answering a question regarding Snape's love life and the redemptive pattern to his character, Rowling expressed her surprise at the foresight.[16] Rowling also disclosed that after the publication of Prisoner of Azkaban, there was one female fan who guessed Snape loved Lily Potter, making Rowling wonder how she had given herself away.[17]

After the completion of the series, Rowling began to speak openly about Snape, discussing the contrast between his character arc and that of Albus Dumbledore.[18] Rowling said "the series is built around [the Dumbledore and Snape storylines]", and maintained that she always knew what Snape would turn out to be at the end and that she carefully plotted his storyline throughout the series. "I had to drop clues all the way through because as you know in the seventh book when you have the revelation scene where everything shifts and you realise...what Snape's motivation was. I had to plot that through the books because at the point where you see what was really going on, it would have been an absolute cheat on the reader at that point just to show a bunch of stuff you've never seen before."[17] Rowling further said in an interview that she wanted Snape to find redemption and forgiveness: "Snape is a complicated man...he was a flawed human being, like all of us. Harry forgives him...Harry really sees the good in Snape ultimately... I wanted there to be redemption."[19]